PSTN (Public Switching Telephone Network) devices, such as POTS (Plain Old Telephone Switch), Carrier Switches, PBX (Private Branch Exchange) switches, NASes (Network Access Servers), etc. are all interconnected using TDM (Time Division Multiplexed) trunk connections to transmit voice and data between them. Furthermore, these network devices require a call manager to communicate between the various endpoints to accurately manage the actual voice or data payload on each of the connections. Call management is achieved with the use of signaling to relay call information between the different endpoints. This signaling is in addition to the actual voice or data payload that is transferred over the telephone network. For example, this signaling can transfer the phone numbers used in the telephone network to establish the connection links within the network to interconnect two or more end user devices, such as phones, together. In other examples, this signaling is used to inform the other endpoint of resource availability.
Various signaling protocols and architectures are used to interconnect devices within the PSTN. Over the years, little has changed with respect to the actual voice or data payload transfer over a DS0 timeslot on a TDM (Time Division Multiplexing) trunk. A DS0 timeslot is a single channel on the physical wire: that is, a single call transmitting and receiving between two endpoints. However, the signaling between the various PSTN devices has evolved substantially. Originally, the first digital signaling was designed to be in-band: that is, the signaling shared the DS0 timeslot with the actual voice or data payload. These TDM trunks were known as PTS (Pulse Trunk Signaling) trunks. Various flavors of PTS trunks have evolved in different geographical markets to address national regulatory and market requirements.
Eventually, architectural problems related to the fact that the signaling was in-band were discovered: e.g., blue-box fraud. New signaling architectures evolved to address these problems. PRI (Prime Rate Interface) and BRI (Basic Rate Interface) trunks provide dedicated timeslots within a trunk for signaling; thus, the signaling does not have to share a common medium with the voice and data payload such as PTS trunks. Newer signaling architectures such as SS7 (Signaling System 7) have further changed the PSTN architecture, doing the signaling on a separate communication network, giving more connectivity and management functionality than previously possible at a network-wide level. All the signaling formats are predominantly standardized and do not deviate from the standard. Furthermore, flavors of all these trunk types coexist in the current PSTN architecture. Although PTS trunks are considered old technology, their low lease access rates make them very popular in many PSTN architectures.
One PTS trunk flavor used within PSTN is known as CAS (Channel Associated Signaling). CAS has two components, line supervisory signaling for initiating and terminating calls, and address signaling for communicating the DNIS and ANI. ANI stands for Automatic Number Identification and DNIS stands for Dialed Number Identification Service.
Given a trunk with a known signaling type, the protocol of both the line supervisory and address signaling is known in advance. This is absolutely necessary, as the two device ends of a PSTN link must know how to communicate with each other. For example, a T1 CAS trunk with multi-frequency signaling in a DS0 channel is required to use an identical line signaling protocol and a “#ANI*#DNIS*” formatted address signal when passing digit collection information during call setup, where both ANI and DNIS digits are between 0–9.
In certain markets, some PSTN equipment vendors are being requested to implement non-standard address signaling protocols on their devices. But where proprietary signaling protocols are implemented, the standard signaling protocols will no longer work. In the past, PSTN network devices were “hard-coded” to recognize the proprietary signaling protocols with which they were expected to intercommunicate. A PSTN network device “hard-coded” to recognize a specific proprietary signaling protocol must be re-coded if a new proprietary signaling protocol is required for a particular market. Furthermore, a PSTN device using a standardized signaling protocol will have to be re-coded if the standardized signaling protocol changes to a proprietary one.
The present invention addresses this and other problems.